The present invention relates generally to closed loop belt tensioning mechanisms, and more particularly, to a closed loop belt tensioning and detensioning assembly for enabling safe, efficient and controlled, non-slipping removal and reinstallation of a flexible closed loop photoreceptor belt within an electrostatographic reproduction machine.
The invention as such can be utilized in the art of xerography, in the printing arts, or in any machine having a tensioned closed loop belt which from time to time requires removal and reinstallation. The invention however will be described in detail with reference to xerography.
In the practice of conventional xerography, it is the general procedure to form electrostatic latent images on a xerographic surface by first uniformly charging a photoreceptor. The photoreceptor comprises a photoconductive member having a charge retentive surface. The charge on the charge retentive surface is then selectively dissipated in accordance with a pattern of activating radiation corresponding to original images. The selective dissipation of the charge leaves a latent charge pattern on the charge retentive or imaging surface corresponding to an electrostatic latent image that is equivalent to the areas not exposed by radiation.
After the electrostatic latent image is formed or recorded as such on the surface of the photoconductive member, it is subsequently developed by bringing a developer material including toner particles into contact therewith, to thereby form toner images on the surface of the photoconductive member. The images are generally then transferred to a support surface such as to plain paper to which they may be permanently affixed by heating or by the application of pressure or a combination of both.
In addition to the charge retentive layer already mentioned, the photoconductive member includes several other layers each having sensitive and life-limited electrical and electrostatic characteristics that wear out with prolonged use. As such it is a common practice to replace the photoconductive member of a xerographic machine after so many thousand images have been formed and transferred from it in the manner described above. Photoconductive members as such can be in the form of a drum or more commonly in the form of an endless loop belt that is trained and tensioned around a support frame. In either case, every so often, such a drum and a belt loop photoconductor has to be removed and a new one reinstalled from the xerographic or electrostatographic machine.
Typically, conventional xerographic and other machines having a tensioned closed loop belt module employ complicated and expensive mechanisms for positioning the belt module""s tensioning roll for the purpose of installing and removing the belt relative to its frame. Such mechanisms can consist of a handle, cables, a pivoting device and several linkages which take up and waste a significant amount of valuable space inside the belt module.
In electrostatographic such machines, whether a vertical or horizontal design, flexible photoreceptor belt loading and unloading onto a photoreceptor belt module requires the detensioning of an idler roll plus the ability to provide removal or installation of the flexible photoreceptor belt without damage. To do this, a tension roll or idler roll must move so as to release the flexible photoreceptor belt, but also in a manner that enables safe, efficient and controlled, non-slipping removal and reinstallation.
In accordance with the present invention, there is provided a tensioning and detensioning assembly includes a frame and a moveable tensioning roll for tensioning the continuous loop belt. The moveable tensioning roll has an axis, a first end, a second end, a first position for tensioning the continuous loop belt, and a second position when the continuous loop belt is detensioned. When the moveable tensioning roll is in the second position the first end is spaced a first distance from the first position, and the second end is spaced (from the first position) a second distance that is different from the first distance in order to enable safe, efficient and controlled, non-slipping removal and reinstallation of the flexible closed loop photoreceptor belt. The tensioning and detensioning assembly also includes a first moving means for moving the moveable tensioning roll into the first position, and a second moving means for moving the first end through the first distance, and the second end through the second distance, thus moving the moveable tensioning roll into the second position, and thereby enabling controlled and non-slipping removal and reinstallation of the belt or photoreceptor.